Cold Working Lubricant and Cold Working Method for Steel Pipe

ABSTRACT

The present invention provides a lubricant comprising an alkali soap and a cold working method, in which the lubricant layer can be easily formed on the surface of a steel pipe prior to cold working the reduces the work load during cold working of the steel pipe, and whose layer can be easily removed by washing the surface of the steel pipe after cold working. After that, an alkali soap aqueous solution or aqueous pasty alkali soap is applied to the working surface of the steel pipe, cold working of the steel pipe is performed, and thereafter the alkali soap layer is removed by washing with water. The alkali soap aqueous solution or aqueous pasty alkali soap is preferably prepared within a vessel having an inner surface consisting of a non-metal material.

FIELD OF THE INVENTION

The present invention relates to a cold working lubricant and a coldworking method for steel pipe. More specifically, the present inventionrelates to a lubricant excellent in lubricating property during coldworking of a steel pipe and excellent in washing removability from thesteel pipe surface after cold working, and a cold working method forsteel pipe using the same.

BACKGROUND OF THE INVENTION

In cold working of a steel pipe, lubricating treatment has been executedfor the purpose of reducing a working load and preventing a seizurebetween the steel pipe and a working tool.

Three methods have been conventionally known for the lubricatingtreatment in cold working of a metal material including the steel pipe,namely, a chemical treatment method, an oil lubricating method and asynthetic resin layer lubricating method.

The chemical treatment method comprises a chemical treatment processsuch as pickling for removing an oxide layer or a hydroxide layer formedon a surface of a metal material, and a layer process for forming asubstrate layer such as a phosphate layer or an oxalate layer, followedby a process for forming a metal soap layer including a non-alkali metalsuch as Zn on the substrate layer. The substrate layer and the metalsoap layer are formed on a work piece surface through these processes.The layer formed by the chemical treatment has an excellent lubricatingproperty. The chemical treatment method is frequently used for apretreatment, mainly for the cold working of a steel wire rod or a steelbar.

The oil lubricating method comprises coating lubricating oil such asmineral oil to a working surface of metal material. The cold working isperformed after coating the lubricating oil. The oil lubricating methodamong the lubricating treatment methods is extensively used for coldworking because the lubricating oil that forms a lubricant layer can beeasily coated. The oil lubricating method is applied mainly to pipeexpansion work, diameter reducing work, cold drawing work, cold rollingand the like of steel pipe.

The synthetic resin layer lubricating method comprises forming asynthetic resin layer on a working surface. This synthetic resin layerfunctions as a lubricant during cold working. The synthetic resin layerlubricating method is applied mainly to press working of the steel sheetor the like.

However, all these lubricating treatment methods have problems asdescribed below. Particularly, the application to lubricating treatmentsin the cold working of a steel pipe is problematic.

The chemical treatment method cannot be adopted except for cold workingof a steel wire rod or a steel bar, because it includes many processesfor forming a substrate layer and thus requires large-scaled facilitiesand troublesome works. In the synthetic resin layer lubricating method,in order to prevent peeling of the synthetic resin layer during coldworking, the synthetic resin layer is needed to be firmly adhered to thesurface of the metal material, which results in an increased cost causedby an enlarged scale of facilities and a troublesome work. Therefore,this method would not be adopted except for cold working of a steelsheet.

On the other hand, the oil lubricating method requires neither atroublesome work nor an enlarged scale of facilities, compared with thechemical treatment method and the synthetic resin layer lubricatingmethod. However, the oil lubricating method does not reduce the workingload more than the chemical treatment method or the synthetic resinlayer lubricating method. In the oil lubricating method, because thelubricating oil is simply coated to the working surface of the metalmaterial, the lubricating oil such as mineral oil that is applied to thesurface of the metal material is low in the adhesiveness, and may notadhere to the part of the surface of the metal material. It results inseizing on this part.

In all theses lubricating treatment methods, it is difficult to removethe lubricant or the lubricating oil from the surface of the metalmaterial after cold working. Accordingly, some lubricant or lubricatingoil is apt to remain on the surface of the resulting metal product afterremoval treatment thereof. The remaining lubricant or lubricating oilmay cause various problems in a heat treatment process or the like afterthe cold working.

When a metal material with a chemical treatment layer consisting of aphosphate remaining on the surface is heat-treated, for example, aphosphorization to the metal material may deteriorate the materialstrength. Remaining lubricating oil on stainless steel material,consisting of mineral oil, causes carburization to the stainless steelproduct during heat treatment. When a metal soap layer containing anon-alkali metal salt of Zn, Mn or the like remains on the surface, thesame problem is caused during heat treatment. Namely, the lubricantremaining on the surface may deteriorate the mechanical characteristicsof the surface of the metal product during heat treatment. Further,since the lubricating oil or synthetic resin layer is regarded as dirt,the product with remaining on the surface cannot be sold thereafter.Because of this problem, the lubricant layer or lubricating oil formedby the lubricating treatment must be removed after cold working. It ispreferable that the lubricant or lubricating oil for cold working of ametal material can be easily removed from the surface of the metalmaterial after cold working, in addition to the excellent lubricatingproperty in the cold working of the metal material.

Besides the three lubricating treatment methods described above, amethod, which is related to the press working of an aluminum plate, isdisclosed in Patent document 1. This method comprises a liquid lubricantconsisting of a mixture of fine lubricant particles such as molybdenumdisulfide and graphite with metal soap applied to the working surface ofan aluminum plate, prior to press working However, this method aims atpress working of a sheet metal such as the aluminum plate with extremelylow cold deformation resistance, and is scarcely applicable to thelubricating treatment for cold working of a pipe-shaped metal, whichinvolves harsh plastic deformation in addition to high cold deformationresistance, such as a cold working of steel pipe including pipeexpansion work or cold drawing work. Furthermore, the lubricantdisclosed in Patent document 1 is difficult to be removed, and when itis applied to the lubricating treatment during the cold working of asteel pipe, particularly, the fine lubricant particles such asmolybdenum disulfide and graphite are scarcely removed from the steelpipe surface. Because, when the oxide or a hydroxide layer is formed onthe surface of the steel pipe, a minute unevenness or crack is apt tooccur on the oxide or hydroxide layer, which would trap fine particlesof the lubricant such as molybdenum disulfide and graphite cannot beremoved.

In relation to the working of the aluminum plate, a solid lubricantmethod is disclosed in Patent Document 2. This method requires a solidlubricant consisting of 3-18% surfactant, 0.03-4.0 wt % rust preventiveagent, and the balance of a water-soluble or water-dispersible filmforming component such as an α-olefin/maleic monoester/maleic acidmonoester salt terpolymer that is a polymeric synthetic wax having amolecular weight of 6000 or more, a carboxylated organic polymercompound having a molecular weight of 1000 or more and a salt thereof.However, this costly solid lubricant, although used for warm pressworking of a sheet metal such as an aluminum plate with an extremely lowcold deformation resistance, cannot be applied to the lubricatingtreatment for cold working of a pipe-shaped metal such as pipe expansionwork or cold drawing work with a high cold deformation resistance, whichrequires a harsh plastic deformation.

Patent Document 1: Japanese Patent Unexamined Publication No. H6-277766.Patent Document 2: Japanese Patent Unexamined Publication No. 6-264086

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

Due to these circumstances, one objective of the present invention is toprovide a cold working lubricant for a steel pipe, which much reducesthe work load on the cold working of a steel pipe, which can easily forma lubricant layer on the surface of the steel pipe prior to coldworking, and is excellent in washing removability thereof from the steelpipe surface after cold working.

Another objective of the present invention is to provide a cold workingmethod for the steel pipe using this lubricant.

Means for Solving the Problems

As a result of examinations and experiments for various lubricants fromthe viewpoint of an easy formation of a lubricant layer onto a surfaceof a steel pipe prior to cold working and easy removal, the presentinventors obtained the following knowledge, focusing in alkali soap.

The alkali soap means a water-soluble alkali metal salt (Na salt or Ksalt) of long-chain fatty acid. The alkali soap can be easily coated tothe working surface of a steel pipe by making it into an alkali soapaqueous solution because it is water-soluble. The layer formed on theworking surface of the steel pipe exists as a lubricant layer on thesurface of the steel pipe as it is or in a dried state, while thelubricant layer after cold working can be easily removed by washing thesurface of the steel pipe with water or hot water after cold working,because it forms the water-soluble alkali soap.

Otherwise, instead of the alkali soap in the state of an alkali soapaqueous solution, an aqueous pasty alkali soap that has some flowabilitycan be coated to the working surface of the steel pipe. Impregnating thealkali soap with water makes this aqueous pasty alkali soap. This is,due to the pasty, conveniently used when the coating is performed toonly a part of the working place that requires a lubricant layer. Theaqueous pasty alkali soap layer after drying is the same as the alkalisoap aqueous solution layer after drying.

The alkali soap is a water-soluble alkali metal salt (Na salt or K salt)of long-chain fatty acid as described above, and any straight chainfatty acid is adoptable thereto regardless of whether the saturatedfatty acid or unsaturated fatty acid. Preferably, the alkali soap iscomposed of either or both of Na salt and K salt of one or more kinds ofstraight-chain fatty acids having 10 to 18 carbon atoms. Specificexamples thereof include such as capric acid (C₉H₁₉COOH), lauric acid(C₁₁H₂₃COOH), myristic acid (C₁₃H₂₇COOH), palmitic acid (C₁₅H₃₁COOH),palmitoleic acid (C₁₅H₂₉COOH), margalinic acid (C₁₆H₃₃COOH), stearicacid (C₁₇H₃₅COOH), oleic acid (C₁₇H₃₃COOH), and linoleic acid(C₁₇H₃₁COOH).

With respect to coating the alkali soaps having various chemicalcompositions on a surface of a steel pipe, lubricating property andwashing removability thereof were examined. The result is shown blow.

The alkali soaps, having chemical compositions shown in Table 1, wereprepared.

TABLE 1 Sample Sample Sample Sample Sample Sample Alkali soap No. 1 No.2 No. 3 No. 4 No. 5 No. 6 Na caprate —  3 — — — — Na laurate 30 23 — — —— Na myristirate 10 35  2 — —  2 Na palmitate 30 38 38  2 5 18 Napalmitoleate — —  4  7 6  4 Na stearate —  1 15 — 7 35 Na oleate 30 — 3775 68  37 Na linorate — —  4 16 14   4

For each of the alkali soap layers, a pendulum friction test wasperformed and the lubricating property concerned was evaluated bymeasuring the frictional coefficient. The test conditions are asfollows.

Each of various alkali soaps having chemical compositions shown in Table1 was dissolved in water to prepare an alkali soap aqueous solution withconcentration of 11 mass %. A specimen ball was covered with thisaqueous solution and dried with cold air to form a layer, and africtional coefficient (μ) thereof was measured. The measurements were30 times performed for each specimen at a room temperature (25° C.).Table 2 shows the friction coefficient in the first measurement and thefriction coefficient as a stabilized value for each sample. For a samplewhose friction coefficient exceeded 0.3μ before the final measurement,the number of times of measurement until the friction coefficientexceeded 0.3μ was shown.

TABLE 2 Friction Friction Number of times of coefficient (μ) coefficientmeasurement until in 1^(st) (μ) as stabilized the friction coefficientmeasurement value exceeded 0.3μ Sample No. 1 0.089 0.448 11 Sample No. 20.158 0.387 19 Sample No. 3 0.097 0.100 — Sample No. 4 0.101 0.104 —Sample No. 5 0.110 0.300 13 Sample No. 6 0.102 0.105 —

Regarding the washing removability of each layer, a specimen having eachlayer in a dried state was washed in water with slightly stirring, andthe adhesion amount of the layer was measured before and after washing,whereby the degree of washing removal was evaluated. The formingcondition and test condition of the specimen are as follows.

Each of various alkali soaps having chemical compositions shown in Table1 was dissolved in water to prepare an alkali soap aqueous solution withconcentration of 11 mass %. This aqueous solution was coated by sprayingonto one side of a SUS thin plate specimen (80 mm×60 mm×1 mm) with alayer thickness of about 30 g/m² (in dried state), followed by dryingfor 24 hours by use of a dryer of 50° C., whereby a dry layer was formedon the specimen. The specimen with the dry layer was dunked in a waterbath (1000-mL beaker) of 50° C. under stirring (just to whirl), and thetime (sec) for the removal of the layer by washing was measured. Thewashing removal time of each specimen is shown in Table 3.

TABLE 3 Washing time (sec) Sample No. 1 10-15 Sample No. 2 15-20 SampleNo. 3 30-40 Sample No. 4 20-30 Sample No. 5 20-25 Sample No. 6 40-50

Consequently, it was found that a layer can be easily formed on aworking surface by coating water-soluble alkali soap thereto, and theresulting layer is excellent in lubricating properties with a lowfriction coefficient. Further, when such a layer is formed, it is alsoeasy to remove the layer by washing after cold working.

The present invention has been achieved based on the new knowledgeabove. The cold working lubricants for a steel pipe according to thepresent invention are shown in the following (1) to (3). The coldworking methods for a steel pipe according to the present invention areshown in the following (4) to (12). Hereinafter each one will bereferred to as the present invention (1) to (12), respectively. Thesemay collectively be referred to as the present invention.

(1) A cold working lubricant for a steel pipe, comprising alkali soap.

(2) The cold working lubricant for a steel pipe according to (1) above,wherein the cold working of a steel pipe is a pipe expansion work of asteel pipe end using a plug.

(3) The cold working lubricant for a steel pipe according to (1) or (2)above, wherein the alkali soap is composed of either or both of Na saltand K salt of one or more kinds of straight-chain fatty acids having 10to 18 carbon atoms.

(4) A cold working method for a steel pipe, comprising cold workingafter forming a solid alkali soap layer on the working surface of asteel pipe by coating an alkali soap aqueous solution thereto.

(5) A cold working method for a steel pipe, comprising cold workingafter forming a solid alkali soap layer on the working surface of asteel pipe by coating an alkali soap aqueous solution thereto followedby drying.

(6) The cold working method for a steel pipe according to (4) or (5),wherein the alkali soap aqueous solution to be coated to the workingsurface of the steel pipe is prepared by dissolving alkali soap in waterwithin a vessel having an inner surface consisting of a non-metalmaterial.

(7) A cold working method for a steel pipe, comprising cold workingafter forming a solid alkali soap layer on the working surface of asteel pipe by coating an aqueous pasty alkali soap thereto.

(8) A cold working method for a steel pipe, comprising cold workingafter forming a solid alkali soap layer on the working surface of asteel pipe by coating an aqueous pasty alkali soap thereto followed bydrying.

(9) The cold working method for a steel pipe according to (7) or (8),wherein the aqueous pasty alkali soap to be coated to the workingsurface of the steel pipe is prepared by impregnating alkali soap withwater within a vessel having an inner surface consisting of a non-metalmaterial.

(10) The cold working method for a steel pipe according to any one of(4) to (9) above, wherein the solid alkali soap layer on the workingsurface is removed after cold working of the steel pipe, by washing theworking surface with water or hot water.

(11) The cold working method for a steel pipe according to any one of(4) to (10) above, wherein the cold working of the steel pipe is a pipeexpansion work of the steel pipe end using a plug.

(12) The cold working method for a steel pipe according to any one of(4) to (11) above, wherein the alkali soap is composed of either or bothof Na salt and K salt of one or more kinds of straight-chain fatty acidshaving 10 to 18 carbon atoms.

The alkali soap referred to herein means alkali metal salt (Na salt or Ksalt) of water-soluble long-chain fatty acid as described above. Anystraight-chain fatty acid can be used thereto regardless of whether asaturated fatty acid or an unsaturated fatty acid. Particularly, thealkali soap is preferably composed of either or both of Na salt and Ksalt of one or more kinds of straight-chain fatty acids having 10 to 18carbon atoms. Specifically, Na or K salts of capric acid (C₉H₁₉COOH),lauric acid (C₁₁H₂₃COOH), myristic acid (C₁₃H₂₇COOH), palmitic acid(C₁₅H₃₁COOH), palmitoleic acid (C₁₅H₂₉COOH), margalinic acid(C₁₆H₃₃COOH), stearic acid (C₁₇H₃₅COOH), oleic acid (C₁₇H₃₃COOH), andlinoleic acid (C₁₇H₃₁COOH) are preferably used. The alkali soap such asthe Na salt and K salt of the water-soluble long-chain fatty acid can beused independently or in combination as well. The cold working lubricantsuch as alkali metal salts of straight-chain fatty acid having 10 to 18carbon atoms of the alkali soaps are preferably used, and the alkalimetal salts of straight-chain fatty acid can be used independently or incombination of two or more kinds thereof.

The cold working lubricant such as the alkali soap may be coated to thesurface of a working tool, but it is preferably coated to the workingsurface of the steel pipe. The cold working can be performed as thelayer formed to the working surface of the steel pipe or to the wetsurface of the working tool, or after drying it.

The steel pipe for cold working includes a stainless steel pipe. Thesteel pipe can be not only a seamless steel pipe manufactured byMannesmann process or Ugine-Sejournet process, but also a hot-forgedsteel pipe or a welded steel pipe.

The cold working method includes pipe expansion work of a steel pipe endusing a plug and drawing work of the steel pipe.

In one cold working method according to the present invention, an alkalisoap aqueous solution is used for a lubricant layer by coating it to theworking surface of a metal material that is not subjected to substratetreatment in order to form a solid alkali soap layer thereon. Althoughthe cold working may be performed as it is, the lubricant layer ispreferably dried prior to the cold working. Thus, the lubricant layercan be easily formed without executing a substrate treatment process inthe chemical treatment. Further, the lubricating treatment method by analkali soap layer reduces workload more than the oil lubricating methodor synthetic resin layer lubricating method. The working surface of thesteel pipe may be in a surface-exposed state by executing descaling byshot blasting or pickling after shaping the metal material by rolling orthe like, or in a state remaining on the surface after rolling with ascale layer that is an oxide or with a rust layer that is a hydroxide.

The alkali soap aqueous solution to be coated to the working surface ofthe steel pipe is preferably prepared by dissolving the alkali soap inwater within a vessel that has an inner surface consisting of anon-metal material. The non-metal material includes, for example, resin,glass, and ceramics. Instead that the vessel itself is made of anon-metal material, only the inner surface of the vessel may be linedwith or coated with the non-metal material. When the alkali soap isdissolved in water within a vessel whose inner surface is in contactwith the alkali soap aqueous solution and consists of a metal materialsuch as zinc (Zn) or tin (Sn), the alkali soap aqueous solution becomessemi-solidified. This semi-solidified alkali soap aqueous solution hasthe property of scarcely adhering to the working surface of the steelpipe. Therefore, it is difficult to coat the working surface with thealkali soap in a uniform thickness, and even if it is dried, a layer allover the whole working surface is scarcely formed. Consequently, thelubricating characteristic is deteriorated, and a seizure may be causedduring working on the surface having no layer. The alkali soap aqueoussolution should be prepared within the vessel whose inner surface iscovered with a non-metal material, whereby the semi-solidification ofthe alkali soap aqueous solution can be prevented, and the adhesivenessof the alkali soap aqueous solution to the working surface is extremelyenhanced. Consequently, the alkali soap can be uniformly coated to theworking surface, and after drying it, a uniform solid alkali soap layercan be formed over the whole working surface.

In another cold working method according to the present invention,aqueous pasty alkali soap is coated to a working surface of a metalmaterial not subjected to substrate treatment in order to form a solidalkali soap layer, whereby it is used as the lubricant layer. Althoughthe cold working may be performed as it is, the lubricant layer ispreferably dried after the coating prior to the cold working. Thus, thelubricating layer can be easily formed without executing a substratetreatment process in chemical treatment. Further, the lubricatingtreatment method by alkali soap layer shows better load reducing effectthan the oil lubricating method or synthetic resin layer lubricatingmethod. The working surface of the steel pipe may be in asurface-exposed state by executing descaling by shot blasting orpickling after shaping the metal material by rolling or the like, or ina state remaining on the surface after rolling with scale layer that isan oxide or with rust layer that is a hydroxide.

The aqueous pasty alkali soap can be prepared by impregnating the alkalisoap with warm water and cooling it to room temperature, then into apasty state, while maintaining the softness to some degree. Thepreferable temperature of the warm water used for the preparation of theaqueous pasty alkali soap is 60° C. or higher. The aqueous pasty alkalisoap to be coated to the working surface of the steel pipe is preferablyobtained by impregnating the alkali soap with water within a vessel thathas an inner surface consisting of a non-metal material. The non-metalmaterial includes, for example, resin, glass and ceramics. Instead thatthe vessel is entirely formed of the non-metal material, only the innersurface of the vessel may be lined with or coated with the non-metalmaterial.

When the inner surface is in contact with the aqueous pasty alkali soapand consists of a metal material such as zinc (Zn) or tin (Sn), theaqueous pasty alkali soap has the property of scarcely adhering to theworking surface of the steel pipe. Therefore, it is difficult to coatthe working surface with the alkali soap in a uniform thickness, andeven if it is dried, a layer all over the working surface is scarcelyformed. Consequently, the lubricating characteristic is deteriorated,and seizure may be caused during working on the surface having no layer.The aqueous pasty alkali soap should be prepared within a vessel whoseinner surface is coated with the non-metal material, whereby theadhesiveness of the aqueous pasty alkali soap to the working surface isextremely enhanced. Consequently, the alkali soap layer can be uniformlyformed on the whole working surface.

In the present invention, the aqueous pasty alkali soap to be coated tothe working surface of the steel pipe is preferably obtained byimpregnating the alkali soap with water within a vessel having an innersurface consisting of a non-metal material. The non-metal materialincludes, for example, resin, glass and ceramics.

When the alkali soap is impregnated with water within a vessel whoseinner surface in contact with the aqueous pasty alkali soap consistingof a metal material, for example, such as zinc (Zn) or tin (Sn), theaqueous pasty alkali soap is scarcely adhered to the working surface ofthe steel pipe. Naturally, the lubricating characteristic isdeteriorated, and seizure is caused during working on the surface havingno layer. The aqueous pasty alkali soap is prepared within the vesselwhose inner surface is covered with the non-metal material, whereby theadhesiveness of the alkali soap aqueous solution to the working surfaceis extremely enhanced.

Since the alkali soap is easily dissolved in water, the working surfaceis washed with water or hot water after cold working, whereby the solidalkali soap layer remaining on the working surface can be easilyremoved. Consequently, the remaining lubricant layer can be suppressedor solved.

The steel pipe to which the cold working lubricant comprising alkalisoap is coated includes a stainless steel pipe. The steel pipe can benot only a seamless steel pipe manufactured by Mannesmann process orUgine-Sejournet process but also a hot-forged steel pipe or a weldedsteel pipe.

The cold working method for the steel pipe includes pipe expansion workof a steel pipe end using a plug, drawing work of steel pipe and thelike.

EFFECT OF THE INVENTION

According to the present invention, a layer of lubricant can be easilyformed on the surface of a steel pipe prior to cold working with a highload reduction effect in cold working of the steel pipe, and the layercan be easily removed by washing of the steel pipe surface after coldworking.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail inreference to the attached drawings. In the drawings, descriptions foridentical or corresponding parts are omitted by assigning the identicalreference number thereto.

The cold working lubricant and cold working method for the steel pipewill be described below. The cold working of the steel pipe is a pipeexpansion work of a steel pipe end using a plug.

In FIG. 1, an alkali soap aqueous solution of a lubricant is prepared(S1). Specifically, the alkali soap of Na salt and/or K salt ofstraight-chain fatty acid are prepared. A preferable main component ofthe alkali soap is Na stearate. The content of the Na stearate in thealkali soap may be such that the effect of the present invention can beshown. Preferably, the alkali soap contains 95 mass % or more of Nastearate.

The above-mentioned alkali soap is dissolved in water within a vesselthat has an inner surface coated with a non-metal material in order toprepare the alkali soap aqueous solution. The non-metal material means,for example, resin such as plastics, glass or ceramics. When the alkalisoap is dissolved in water within a vessel that has an inner surfaceconsisting of a metal material such as a metal vessel, the alkali soapaqueous solution becomes semi-solidified. Such an alkali soap aqueoussolution scarcely adheres to the working surface (inner surface or outersurface) of a steel pipe, and even if it could adhere to the workingsurface, the resulting layer is not uniform but uneven. Therefore, it isextremely difficult to uniformly coat the alkali soap onto the wholeworking surface. Although the cause of this is not necessarily certain,the following explanation should be considered. When solid alkali soapis dissolved in water within a vessel that has an inner surfaceconsisting of a metal material, the metal element constituting thevessel inner surface is dissolved in the alkali soap aqueous solution.During this time, the dissolved metal element is bonded with long-chainfatty acid of the alkali soap to produce a metal soap (non-alkali metalsalt of the long-chain fatty acid). This generation of metal soap causesconsiderably deterioration of the adhesiveness to the working surface.

Therefore, the alkali soap aqueous solution should be prepared within anon-metal vessel. The alkali soap aqueous solution can be uniformlyadhered to the entire working surface with good adhesiveness. Increasingthe amount of alkali soap added to the water results in increasing theviscosity of the alkali soap aqueous solution, and improves theadhesiveness to the working surface. When the alkali soap concentrationin the alkali soap aqueous solution is set at 100 g/L (liter) to 450g/L, the resulting alkali soap aqueous solution shows satisfactoryadhesiveness. Even out of this concentrated range, the alkali metal soapaqueous solution is adhered to the entire working surface so that theeffect of the present invention is displayed to certain degree.

The alkali soap aqueous solution prepared within the non-metal vessel isapplied to the working surface that is not subjected to chemicaltreatment (S2). Specifically, the alkali soap aqueous solution isdirectly applied to an inner or outer surface of a steel pipe with ascale layer that is an oxide or rust layer, which is a hydroxide adheredthereto after rolling, or an inner or outer surface of a steel pipe freefrom scale or rust (or base metal surface) which is subjected todescaling or derusting treatment.

A chemical treatment layer formed by a chemical treatment (phosphatelayer, oxalate layer, and metal soap layer) is scarcely removed aftercold working since it is adhered to the steel pipe surface by chemicalbonding. If the chemical treatment layer is left on the steel pipe inneror outer surface, mechanical characteristics of the steel pipe candeteriorate. For example, when a steel pipe's remaining zinc phosphatelayer on the inner or outer surface is heat-treated or welded to anothersteel pipe, phosphorization can be caused and this may reduce thestrength of the steel pipe. If oil of the oil lubrication methodremains, the non-fitting of paint may cause a line pipe which connectssteel pipes with the steel pipe inner or outer surface, from beingpainted. Therefore, in this situation, it is preferable to use a steelpipe that has not been subjected to chemical treatment or to oillubrication.

The alkali soap solution is coated to a working surface of a steel pipe,for example, by the following methods. A worker such as an operator of apipe expansion apparatus coats the alkali soap aqueous solution to theworking surface by use of a brush or the like. Otherwise, the alkalisoap aqueous solution may be coated to the working surface by dunkingthe steel pipe itself in the alkali soap aqueous solution within anon-metal vessel.

After the alkali soap aqueous solution is coated to the steel pipe'sinner surface, the alkali soap aqueous solution is dried to form a solidalkali soap layer (S3). Since the alkali soap is applied closely to allof the working surface and results in a solid layer when dried, dryingis preferably performed. The drying can be performed, for example, byuse of a blower or the like for quick drying or by natural drying in theatmosphere.

After the solid alkali soap layer is formed, the resulting steel pipe isexpanded (S4). At this time, the steel pipe whose inner surface has thesolid alkali soap layer formed thereon is expanded in contact with aplug that is a working tool. The solid alkali soap layer has a higheradhesiveness to the working surface than the lubricating oil used in theconventional oil lubrication. Further, the oil escapes toward the lowerpressure side when working pressure is applied because it is a fluid,resulting in deterioration of the lubricating performance. The solidalkali soap layer has poor flowability because it is solid and staysthere even if the working pressure is applied. Therefore, the solidalkali soap layer can prevent direct contact to the steel pipe with thetool, which is more satisfactory in both lubricating property andseizure resistance, than in the oil lubrication. Consequently, flawingin the working surface can be prevented. Further, the lubricating by asolid alkali soap layer can reduce the workload more than the oillubrication.

After the cold working, the working surface is washed with water toremove the solid alkali soap layer (S5). Since the alkali soap easilydissolves in water, the solid alkali soap layer adhered to the workingsurface can be easily removed by washing with water. Therefore, comparedwith the conventional lubricating treatment, the lubricant layer ismostly removed. Since the dissolution degree of alkali soap increases byraising the temperature of the water for washing, and even though thewater temperature may be normal, the time necessary for removal can bealso shortened. Namely, the alkali soap can be removed in a short timeby washing with hot water.

In the cold working method according to the present invention, usingalkali soap for the lubricant can easily form a lubricant layer.Therefore, the use of a plurality of different processes is not neededfor forming the lubricant layer (chemical treatment layer) in comparisonwith the chemical treatment method, and is not needed for facilities forproducing a substrate layer such as phosphate layer. The presentinvention reduces the workload more than the conventional oillubrication or synthetic resin layer lubrication.

Further, the solid alkali soap layer that is the lubricant layer in thepresent invention can be easily removed by washing with water.Therefore, the lubricant layer can be removed more easily than in theconventional lubricating treatments (chemical treatment, oil lubricationand synthetic resin layer lubrication), and the remaining lubricantlayer on the working surface of a metal product can be considerablyremoved.

Comparing the lubricant layers (chemical treatment layer, lubricatingoil and synthetic resin layers) formed in the conventional lubricatingtreatments, the lubricant layer coated by the alkali soap in the presentinvention has a small environmental problem. Also the detergent used forremoving the chemical treatment layer or lubricating oil has not only alarge environmental problem, but also harmfully influences the humanbody. The lubricant layer according to the present invention can beeasily removed with water, so that the environment and human bodyproblems can be significantly reduced.

Instead of the alkali soap aqueous solution that is coated on theworking surface mentioned above, the aqueous pasty alkali soap can beapplied. Impregnating solid alkali soap with warm water and cooling toroom temperature can be used to prepare the aqueous pasty alkali soap.The temperature of warm water is preferably 60° C. or higher and, morepreferably, 80° C. or higher. The aqueous pasty alkali soap ispreferably prepared within a vessel having an inner surface consistingof a non-metal material. The hardness of the aqueous pasty alkali soapis lower than general solid alkali soap, and substantially equal to, forexample, the hardness of lipstick.

The aqueous pasty alkali soap prepared by the above-mentioned method isapplied to a working surface of a steel pipe in the same manner as thealkali soap aqueous solution. The aqueous pasty alkali soap is solidhaving no flowability. Therefore, the aqueous pasty alkali soap can beeasily applied to the working surface, particularly only to a place thatrequires a lubricant layer on the surface of the steel pipe. The aqueouspasty alkali soap is easy to adhere to the working surface because ofit's low hardness, and thus can be easily uniformly coated.

The cold working is preferably carried out after drying the aqueouspasty alkali soap applied to the working surface.

Although the cold working is carried out at a normal temperature in theabove-mentioned conditions, the present invention is applicable to hotworking which is carried out by heating a steel pipe to a temperature of150° C. or lower, which has the same effect as above.

Example 1

A seamless steel pipe was subjected to pipe expansion using Na stearateas a lubricant, and the load applied in the pipe expansion was examined.

A seamless steel pipe with a shape and a strength (grade) shown in Table4 (hereinafter simply referred to as steel pipe) was prepared. In thetable, the unit of outside diameter, inside diameter, pipe thickness andlength are shown by mm, and the grade is based on the API standard. Thematerial of the steel pipe is carbon steel.

TABLE 4 Shape Outside Inside diameter Pipe thickness Length diameter(mm) (mm) (mm) (mm) Grade 89.05 75.33 6.86 150 5CT3-P110

Three pipe expansion plugs 1 of a shape shown in FIG. 2 were prepared. Alayer of 3 mm thickness was formed respectively on the surface 10 tocontact with the inner surface of the steel pipe of each plug 1, usingthe materials and formation method shown in Table 5.

TABLE 5 Plug No. Layer material 1 Cemented carbide 2 SKD steel 3 CrNlayer by ion plating

The plug of Plug No. 1 is a cemented carbide plug. The plug of Plug No.2 is made of cold working tool steel (SKD steel). The plug layer of PlugNo. 3 is CrN layer formed by ion plating. The maximum value of the plugdiameter of each plug 1 is 76.8 mm.

The pipe expansion work was executed by use of an apparatus shown inFIG. 3 according to the following method. A steel pipe 2 was fixedbetween the plug 1 and a cylindrical pushing and pulling tool 4. Afterfixing, the pushing and pulling tool 4 was pushed by a press head 3 of a150-t press machine arranged on the opposite side of the steel pipe 2across the pushing and pulling tool 4, whereby the steel pipe 2 waspushed into the plug 1. At this time, the steel pipe 2 was pushed untilthe plug 1 was passed through the whole length of the steel pipe 2. Thepipe expansion ratio was 2.0% in each case.

The 150-t press machine is provided with a load cell, and the workingload in the pipe expansion was determined using the load cell.

The pipe expansion work was performed while variously changing thecondition of lubricant. The test condition is shown in Table 6.

TABLE 6 Test Lubricant condition Steel pipe inner surface Plug surface 1Non Non 2 Mineral oil Non 3 Water Non 4 Non Na stearate (not dried) 5 Nastearate (not dried) Na stearate (not dried) 6 Na stearate (dried) Non 7Na stearate (not dried) Non

As shown in Table 6, in Test condition 1, the pipe expansion was carriedout without coating any lubricant to the steel inner surface. In testcondition 2, the pipe expansion was carried out after coating mineraloil (manufactured by Idemitu Kosan, SD22) to the whole steel pipe innersurface. In Test condition 3, the pipe expansion was carried out aftercoating water as lubricant to the whole steel pipe inner surface. InTest condition 4, the pipe expansion was carried out after coating Nastearate aqueous solution with concentration of 100 g/L (liter) aslubricant to the plug surface and substantially perfectly drying andsolidifying the lubricant by air blowing for 10 minutes. No lubricantwas coated to the steel pipe inner surface in Test condition 4. In Testcondition 5, the same Na stearate aqueous solution as in Test condition4 was coated to the whole steel pipe inner surface and to the whole plugsurface, thereafter the pipe expansion was performed before the coatedNa stearate aqueous solution was dried. In Test condition 6, the pipeexpansion was carried out after the same Na stearate aqueous solution asin Test condition 4 was coated to the whole steel pipe inner surface,and dried by air blowing for 10 minutes to form a solid Na stearatelayer. In Test condition 7, the same Na stearate aqueous solution inTest condition 4 was coated to the whole steel pipe inner surface, andthe pipe expansion was carried out before it is dried. The Na stearateaqueous solution of each condition was prepared within a plastic vessel.In the conditions other than Test conditions 4 and 5, no lubricant wascoated to the plug surface.

In each test condition, the pipe expansion was carried out using part orall of the plugs of Plug Nos. 1 to 3.

The test result is shown in FIG. 4. In the drawing, each black bar chartshows the load in pipe expansion using the plug of Plug No. 1. Eachwhite bar chart shows the load in use of the plug of Plug No. 2. Eachinternally hatched bar chart shows the load in use of the plug of PlugNo. 3.

In use of each of the plugs of Plug Nos. 1 to 3, the load was minimizedin Test condition 6. Namely, the load in the pipe expansion could bereduced more in Test condition 6, with the Na stearate layer formed onthe working surface, than in Test condition 2 using mineral oil as inthe conventional pipe expansion work. The load was reduced more in Testcondition 6, in which the coated Na stearate was dried, than Testconditions 4 and 7, in which the pipe expansion work was carried outbefore drying it. This result is attributed to that, since theadhesiveness of Na stearate to the working surface (inner surface) washigher in its dried state, the function of the lubricant was furtherexpressed.

After the pipe expansion work, the inner surface of each steel pipeproduct, which was expanded in Test conditions 2 and 6, was washed withwater. Specifically, a water of normal temperature was injected from anozzle with an inside diameter of 3.6 mm at a rate of 8 L (liter)/min towash the steel pipe's inner surface. Consequently, the mineral oil layercoated in Test condition 2 was scarcely removed, while the Na stearatelayer coated as the lubricant in Test condition 6 was fully removed.

Table 7 is a result of water washing that was separately carried out ata hydraulic pressure of 5 MPa to the Na stearate layer coated as thelubricant in Test condition 6. The washing removability of Na stearatelayer after the pipe expansion work was evaluated by variously changingthe time from the pipe expansion work of the steel pipe end using theplug at the start of washing. At this time, the temperature (° C.) ofthe washing water and the washing time (sec) were varied. Consequently,it could be confirmed that the Na stearate layer can be easily removedby water washing regardless of the temperature of washing water (10-80°C.) and the washing time (20-30 sec) if the washing is started within 1hour after the pipe expansion work.

TABLE 7 Time to start of Temperature Washing washing of washing Washingtime condition after working water (° C.) (sec) Evaluation 1 5 min 10 20◯ 2 5 min 20 20 ◯ 3 5 min 30 20 ◯ 4 5 min 80 20 ◯ 5 1 hour 10 20 ◯ 6 1hour 20 20 ◯ 7 1 hour 30 20 ◯ 8 1 hour 80 20 ◯ 9 3 hours 10 20 X 10 3hours 20 20 Δ 11 3 hours 20 30 ◯ 12 3 hours 30 20 ◯ 13 3 hours 80 20 ◯(Note) Evaluation: ◯: Layer was perfectly removed by washing. Δ: Layerwas almost removed by washing, but partially left. X: Layer was almostleft after washing.

As an additional test, a plurality of alkali soap lubricants, whichdiffered in concentration of Na stearate, was prepared. Specifically,three kinds of alkali soap lubricants of (1) Na stearate aqueoussolution having a concentration of 200 g/L, (2) aqueous pasty Nastearate obtained by impregnating Na stearate with hot water of about80° C. to a concentration of 350 g/L followed by cooling to roomtemperature, and (3) aqueous pasty Na stearate obtained by impregnatingNa stearate with hot water of about 80° C. to a concentration of 450 g/Lfollowed by cooling to room temperature were prepared.

Each of the prepared alkali soap lubricants was coated to the wholeinner surface of the above-mentioned steel pipe and dried by air blowingfor 10 minutes to form Na stearate layer, thereafter the pipe expansionwas carried out. Consequently, in each alkali soap lubricant, the loadreducing effect of the same degree as in the Na stearate aqueoussolution, with concentration of 100 g/L used in Test condition 6, wasobtained.

Example 2

A pipe end of a stainless steel pipe was expanded using Na stearate andconventional mineral oil as lubricants, respectively, and the loadapplied in pipe expansion was examined for each lubricant.

A super-13Cr steel pipe (hereinafter simply referred to as stainlesssteel pipe) with an outside diameter 114.3 mm, a thickness 8.56 mm andan inside diameter 97.18 mm was prepared as a steel pipe material.

A plug used for the pipe expansion was made of cemented carbide. Thisplug has a TD-treated surface and a shape similar to that of FIG. 3. Themaximum plug diameter of the plug is 98.15 mm.

The pipe expansion was carried out according to the following method.Ten stainless steel pipes were prepared, in which the inner surface wasat least within the range of 50 mm from the pipe end and was coated withNa stearate aqueous solution of 100 g/L (liter) uniformly, andsubstantially dried. The Na stearate aqueous solution was preparedwithin a plastic vessel. In order to compare the material, fourstainless steel pipes were prepared, in which the inner surface of thepipe end, within the same range as above, was coated with conventionalmineral oil.

The pipe end portion of 50 mm in length from the pipe end of each steelpipe was expanded at normal temperature, using hydraulic machiningequipment mounted with the above-mentioned plug. The pipe expansion ratewas 1.0%. The maximum value and minimum value of the original pressureof the hydraulic machining equipment in pipe expansion were measured.Based on the measurement result, the average values of the maximum valueand minimum value of original pressure were determined for eachlubricant.

The examination result is shown in FIG. 5. In the drawing, the verticalaxis shows the original pressure (kgf/cm²). In the drawing, each whitebar chart shows the average of the maximum value of original pressure,and each black bar chart shows the average of the minimum value oforiginal pressure. As is referred from FIG. 5, the maximum value andminimum value of the original pressure were lower in the Na stearatethan in the mineral oil.

After the pipe expansion work, the inner surface of each steel pipe waswashed in the same condition as in Example 1. Consequently, only a smallamount of the mineral oil was removed, while the Na stearate was easilyremoved without any remaining.

INDUSTRIAL APPLICABILITY

According to the present invention, a layer of the lubricant can beeasily formed on a surface of a steel pipe prior to cold working, inwhich much reduces the workload during cold working of the steel pipe. Alayer of the lubricant can be also easily removed by washing the steelpipe surface after cold working. The present invention is applicable tocold working, particularly, pipe expansion work of the steel pipe endusing a plug.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing each process of a cold working methodaccording to an embodiment of the present invention.

FIG. 2 is a side view showing the shape of a plug used in Example 1.

FIG. 3 is a schematic view of a pipe expansion apparatus used in Example1.

FIG. 4 is a view showing the pipe expansion load value in each testcondition determined in Example 1.

FIG. 5 is a view showing the original pressure value of hydraulicmachining equipment in each lubricating treatment determined in Example2.

EXPLANATION OF REFERENCE NUMERALS

-   -   1. Plug    -   2. Steel pipe    -   3. Press head    -   4. Pushing and pulling tool

1. A cold working method for a steel pipe, comprising cold working afterforming a solid alkali soap layer on the working surface of a steel pipeby coating an alkali soap aqueous solution thereto.
 2. A cold workingmethod for a steel pipe, comprising cold working after forming a solidalkali soap layer on the working surface of a steel pipe by coating analkali soap aqueous solution thereto followed by drying.
 3. The coldworking method for a steel pipe according to claim 1, wherein the alkalisoap aqueous solution to be coated to the working surface of the steelpipe is prepared by dissolving alkali soap in water within a vesselhaving an inner surface consisting of a non-metal material.
 4. The coldworking method for a steel pipe according to claim 2, wherein the alkalisoap aqueous solution to be coated to the working surface of the steelpipe is prepared by dissolving alkali soap in water within a vesselhaving an inner surface consisting of a non-metal material.
 5. A coldworking method for a steel pipe, comprising cold working after forming asolid alkali soap layer on the working surface of a steel pipe bycoating an aqueous pasty alkali soap thereto.
 6. A cold working methodfor steel pipe, comprising cold working after forming a solid alkalisoap layer on a working surface of a steel pipe by coating an aqueouspasty alkali soap thereto followed by drying.
 7. The cold working methodfor a steel pipe according to claim 5, wherein the aqueous pasty alkalisoap to be coated to the working surface of the steel pipe is preparedby impregnating alkali soap with water within a vessel having an innersurface consisting of a non-metal material.
 8. The cold working methodfor a steel pipe according to claim 6, wherein the aqueous pasty alkalisoap to be coated to the working surface of the steel pipe is preparedby impregnating alkali soap with water within a vessel having an innersurface consisting of a non-metal material.
 9. The cold working methodfor a steel pipe according to any one of claims 1 to 8, wherein the coldworking of the steel pipe is a pipe expansion work of the steel pipe endusing a plug.
 10. The cold working method for a steel pipe according toany one of claims 1 to 8, wherein the alkali soap is composed of eitheror both of Na salt and K salt of one or more kinds of straight-chainfatty acids having 10 to 18 carbon atoms.
 11. The cold working methodfor a steel pipe according to any one of claims 1 to 8, wherein the coldworking of the steel pipe is a pipe expansion work of the steel pipe endusing a plug, and wherein the alkali soap is composed of either or bothof Na salt and K salt of one or more kinds of straight-chain fatty acidshaving 10 to 18 carbon atoms.